All four of these temperature reconstructions show the Medieval Warm Period ~1000 years ago was warmer than the present [year 2000].

Fig. 1. Different estimates of Northern Fennoscandian temperature anomalies between 400-2000 AD. Shown are the present conventional estimate (Ttorn, green) which is rather close to that in Grudd08, the present filtered estimate (Tlong, blue), smoothed temperatures of Esper12 (Tesp, red) and smoothed August SST reconstruction from the Norwegian Sea (black).

The new temperature reconstruction presented by this paper shows the Medieval Warm Period [~1000 years ago] in the Arctic was warmer than the present [year 2000] temperatures. Fig. 4. The present estimate of the climatic temperature anomalies (red, Tclim = Tesp + Tsea + Tvolc), and TespfromFig. 1(thick blue).

Highlights

Abstract

The classical Maximum Density data of 65 Torneträsk trees from years 441-1980 AD are studied in millennial, centennial and volcanic scales. The millennial scale is analyzed applying a specific filtering method. In that scale, the climate is cool after 1200-1400 AD. This more or less steady period is suggested to be due to volcanic episodes, which reduced the northward heat transport in the North Atlantic. The century scale variation, on the other hand, is suggested to be due to [natural] internal oscillations in sea surface temperature (SST) and to be connected to variations in the Arctic sea ice. Specifically, these oscillations have caused an additional warming and cooling trend in Northern Fennoscandian temperatures before and after 1930’s, respectively.

Variations in the temperature estimates are explained by the results for different temporal scales. All of them show local impacts leading to differences when compared with hemispheric estimates. The long-term estimate of the temperature as derived from the present Torneträsk data is found to be biased. The source of that is unknown.